Leetcode 2001. Number of groups of interchangeable rectangles (brute force enumeration failed)

From... With a subscript 0 Start with a two-dimensional integer array rectangles To express n A rectangle , among rectangles[i] = [widthi, heighti] It means the first one i The width and height of a rectangle .

If two rectangles i and j（i < j） Have the same aspect ratio , These two rectangles Interchangeable . A more standardized statement is , Two rectangles satisfy widthi/heighti == widthj/heightj（ Use real division instead of integer division ）, These two rectangles Interchangeable .

Calculate and return rectangles How many of them are right Interchangeable rectangular .

Example 1：

 Input ：rectangles = [[4,8],[3,6],[10,20],[15,30]]
 Output ：6
 explain ： Press the subscript below （ from  0  Start ） List the pairing of interchangeable rectangles ：
-  rectangular  0  And rectangle  1 ：4/8 == 3/6
-  rectangular  0  And rectangle  2 ：4/8 == 10/20
-  rectangular  0  And rectangle  3 ：4/8 == 15/30
-  rectangular  1  And rectangle  2 ：3/6 == 10/20
-  rectangular  1  And rectangle  3 ：3/6 == 15/30
-  rectangular  2  And rectangle  3 ：10/20 == 15/30

Example 2：

 Input ：rectangles = [[4,5],[7,8]]
 Output ：0
 explain ： There are no pairs of interchangeable rectangles .

Tips ：

• n == rectangles.length
• 1 <= n <= 10^5
• rectangles[i].length == 2
• 1 <= widthi, heighti <= 10^5

Code:

class Solution {
    
public:
    long long interchangeableRectangles(vector<vector<int>>& rectangles) {
    
        long long res=0;
    
        int size=rectangles.size();
        for(int i=0;i<size;i++)
        {
    
            for(int j=i+1;j<size;j++)
            {
    
                vector<int>sub1=rectangles[i];
                vector<int>sub2=rectangles[j];
                
                if(sub1[0]*sub2[1]==(sub1[1]*sub2[0]))
                {
    
                    res++;
                }
            }
        }
        return res;
    }
};